Method of and apparatus for electronically simulating the operating characteristics of a fuel-injection system and for designing same

ABSTRACT

The four major elements of a fuel-injection system for a combustion engine, i.e. the pump, metering valve, pressure line, and injector, are simulated by respective electronic analog networks whose various operating characteristics can be adjusted to electronically simulate just the operating conditions of these elements whereby the system design can be optimized by the variation-of-parameters method. The pump analog is a pulse generator. A pulse-shaping network is connected to this generator to form the pulse in analogy to the operation of the metering valve which forms the fluid pulse of the pump. An electronic delay circuit simulates the action of the pressure line and another shaping network replaces the injector. Shunt switches are provided to bypass both the first shaping network and the delay network to duplicate the performance of fuel-injection systems without a metering valve and/or pressure line.

0 United States Patent [1 1 [111 3,760,173 Boita [451 Sept. 18, 1973[54] METHOD OF AND APPARATUS FOR 2,830,179 4/1958 Stenning 328/56ELECTRONICALLY SIMULATING THE 3,007,060 10/1961 Guenther............307/268 3,529,144 9/1970 Patterson et all 235/184 OPERATINGCHARACTERISTICS OF A FUEL-INJECTION SYSTEM AND FOR DESIGNING SAMEInventor: Mibai Boita, Bucharest, Romania Energetice, Bucharest, RomaniaPrimary Examiner-Felix D. Gruber Attorney-Karl F. Ross 57 ABSTRACT Thefour major elements of a fuel-injection system for a combustion engine,i.e. the pump, metering valve, pressure line, and injector, aresimulated by respective electronic analog networks whose variousoperating characteristics can be adjusted to electronically simulatejust the operating conditions of these elements whereby the systemdesign can be optimized by the variation-of-parameters method. The pumpanalog is a pulse generator. A pulse-shaping network is connected tothis generator to form the pulse in analogy to the operation of themetering valve which forms the fluid pulse of the pump. An electronicdelay circuit simulates the action of the pressure line and anothershaping network replaces the injector. Shunt switches are provided tobypass both the first shaping network and the delay network to duplicatethe performance of fuelinjection systems without a metering valve and/orpressure line.

6 Claims, 6 Drawing Figures [22] Filed: Nov. 9, 1971 [21] Appl. No.:196,935

[52] US. Cl 235/184, 235/183, 307/268, 328/36, 328/56 [51] Int. Cl G06g7/57 [58] Field of Search 235/184, 183; 328/56, 127, 34, 35, 36, 53, 58,59; 307/268 [56] References Cited UNITED STATES PATENTS 3,252,098 5/1966Schlaepfer 307/268 3,581,077 5/1971 Damewood et al..... 235/1843,254,233 5/1966 Kobayashi et a1. 328/56 2,503,909 4/1950 Hollingsworth328/56 2,578,273 12/1951 Wachtell 328/56 8 T 2, m. 1 P fi I d I METHODOF AND APPARATUS FOR ELECTRONICALLY SIMULATING THE OPERATINGCHARACTERISTICS OF A FUEL-INJECTION SYSTEM AND FOR DESIGNING SAME FIELDOF THE INVENTION The present invention relates to a method of and anapparatus for simulating the operating conditions of a fuel-injectionsystem for an internal-combustion engine. More particularly thisinvention concerns an electronic analog simulation apparatus and methodwhich can be made to electronically duplicate all the principaloperating characteristcs of such a fuel-injection system to enabledesign of such systems by variation of the respective parameters tooptimize the efficiency of the system.

BACKGROUND OF THE INVENTION A fuel-injection system generally consistsof a pump or the like which delivers a fluid pulse to a control orpressure valve that in turn meters out a charge of fuel through apressure line to an injector. In some arrangements the pump directlyfeeds the fuel through the line to the injector in which case the pumpcan be thought of as also acting as the valve.

In order to design such systems it is necessary to take a multitude ofoperating characteristcs of the various components into account.Specifically the size and frequency of the fluid pulses must be tuned toth e reaction characteristics of the metering valve which in turn mustbe related to the fluid-transmission characteristics of the pressureline. Finally the reaction characteristics of the injector must be takeninto account. Clearly this makes it difficult to calculate, forinstance, just how much time lag will take place between the initialpulse formation at the pump and the final spurt of the fuel into thecylinder or swirl chamber. Simularly it is difficult to calculate justhow much of a pulse must be delivered by the pump to produce a givenfuelcombustion response in the engine cylinders.

As a matter of fact the calculation of the above characteristics haveproven to be such an error-fraught and time-consuming process thatfuel-injection systems have merely been designed by empiricallyreplacing mechanical components until the overall operatingcharacteristics have been optimized. Such method of designing is farfrom ideal, making an examination of a new fuel-injection system so muchtrouble as not to be worth the effort. In addition such a method rarelygives the optimum results. 7

While I have mentioned that a basic fuel-injection system for aninternal-combustion engine generally comprises a source of fuel underpressure, a transmission path for the fuel and a fuel outlet at the endof this transmission path opening into the combustion or engine chamber,and that the parameters of such systems have hitherto been designed bytrial-and-error replacement of the parts of the tramsission line, fuelsource and fuel outlet, I should also mention a problem which arises inelectronic fuel injection. Electronic fuelinjection systems control thetiming of the fuel pulses,

i.e. the triggering of the fuel source or a control valve along thetransmission line, in accordance with cylinder operation modes and mustbe designed in accordance with the response characteristics of themechanical system. The term mechanical system is used herein to refer tothe mechanical components of the fuelinjection system, namely, the pumpor other source of fuel under pressure, the transmission line or pathincluding any valve means provided therealong, and the outlet device ornozzle. At any point along this system, electronic controls may beprovided in accorddance with conventional practice to trigger, throttleor terminate the flow of fuel in accordance with the responsecharacteristics of the fuel-injection system and the timing requirementsof the other parts of the engine. In many cases, the electronic controlof fuel injection establishes the parameters of one of the mechanicalcomponents of the system. e.g. a pump or valve. In this case, it isimportant to determine which parameters of the other components arenecessary to obtain optimum efiiciency of the fuel-injection system.Here again, designers of fuel-injection systems and especiallyelectronic fuel-injection systems were required to operate bytrial-and-error methods, using replacement of the several componentswith respect to the fixed components, to establish the optimumcharacteristics.

I should also like to mention that I am aware that it has been proposedto provide analog systems for simulating mechanical operations and, forexample, electronic analogs of damping and oscillation systems are ,wellknown. As far as I am aware, however, it has not been possibleheretofore to apply similar principles in the design of fuel-injectionsystems because of the particular responses of the various components ofsuch systems. Hence the automatic or convenient variations of parametersof components of a fuel-injection system or analogs thereto have notbeen possible heretofore.

OBJECTS OF THE INVENTION It is therefore an object of the presentinvention to provide an apparatus which allows the simulation of afuel-injection system in order to assist in the design and building ofactual systems. i

A further object is to provide a method of and apparatus for simulatingall of the operating characteristics of a fuel-injection system.

SUMMARY OF THE INVENTION I attain the above and other objects with anelectronic device having four major networks which can be regulated tosimulate the various characteristics of the four elements, i.e. thepump, metering valve, pressure line, and injector, of a fuel-injectionsystem. According to features of the present invention numerouspossibilities of adjustment are provided so that all of the principalkinds of fuel-injection systems can be simulated in an analog apparatusin order that the output can be read on, for instance, an oscilloscopeand the various parameters can be changed until the desired result isobtained.

The analog network simulating the pump of the fuelinjection systemincludes a pulse generator and an impedance. The pulse output of such agenerator can be varied by providing adjustable reactive elementsconnected to the generator output. According to another feature of thepresent invention the shaping network that simulates the valve in thefuel-injection system is basically an integrator comprising a tunedcircuit across which a diode and a load resistor are connected. Insteadof a diode an operational amplifier, which inherently has diodicproperties, with. a variable feedback loop, can be provided. Of courseto simulate fuelinjection systems wherein the pump effectively includesthe valve, this shaping network is bypassed by a shunting switch.

An electronic delay circuit constitutes the network simulating thepressure line. Finally a difierentiating network is provided to take theplace of the injector. Once again the delay circuit can be shunted tosimulate systems wherein the pump is provided directly at the cylinder,or wherein the metering valve is located at this point.

From the foregoing, it is apparent that my invention resides in the useof an analog reproduction of the mechanical components of afuel-injection system to enable the parameters of an actualfuel-injection system to be ascertained with an optimum output andthereby allow improved electronic fuel-injection systems to be developedusing these parameters. Of course, the parameters of interest includethe input parameters, namely, the pulse shape, frequency, timing andamplitude of the electronic signals which are the analogs of the inputfuel pulses generated by the source of a fuelinjection chain.

It is next important to establish the signaltransmission and signalmodification parameters of the transmission line or path between thesource and the outlet of the system and any attenuation, losses orsystem-response or transfer-function characteristics of the transmissionline.

Finally, it is essential to establish the response and correspondingcharacteristics of the outlet or nozzle.

In the system of the present invention, at least three, but preferablymore, quadripoles or bocks are provided in sequence to constitute anelectronic analog of the mechanical system. These blocks include asignal generator block producing an electronic output which is an analogof the time-rate-of change of a parameter of fuel pulse transmitted tothe system, and includes any pulseshaping means (preferably adjustable)between a pulse generator and the output of this block which may benecessary to provide a transfer function analogous to that of the pumpor other fuel source of the mechanical system. While the signal isgenerally a stop upon which a sawtooth has been superimposed,corresponding to the output of a pulse-generating pump, variousattenuators may be provided within the block to more closely representthe fuel signal and even to enable design of an optimum elecronic signalto serve as a guide for design of the pump which will produce thecorresponding fuel signal.

The next block or quadripole of the chain comprises an electroniccircuit having a transfer function which is variable to determineoptimum operating characteristics, but which represents the transmissionpath of the fuel pulse. This transmission line or block may consist oftwo or more subblocks, at least one of which represents a resistance orthrottle by its transfer function, corresponding to the pressurized linealong which the fuel is to flow. Another component of the pathrepresenting the transmission portion of the system may be a block orquadripole representing a metering or other valve. It will be apparent,however, that the control valve may also be incorporated in the source.Since the nozzle generally comprises a valve which ispressureresponsive, i.e. allows a buildup of pressure at a certain leveland then discharges a fuel spurt or jet into the engine, the final blockis a quadripole whose electronic components present the transferfunction of a storage and threshold device.

DESCRIPTION OF THE DRAWING The above and other objects, features, andadvantages will become apparent from the following, reference being madeto the accompanying drawing in which:

FIG. 1 is a block diagram illustrating a fuel-injection system;

FIGS. 2, 3, and 4 are diagrammatic views of three types offuel-injection systems;

FIG. 5 is a schematic diagram of a simplified embodiment of theapparatus according to the present invention; and

FIG. 6 is a schematic diagram of a more complicated embodiment of theapparatus according to this invention.

SPECIFIC DESCRIPTION As shown in FIG. 1 a fuel-injection system consistsof a pump A connected through a metering valve B and a pressure line C,to an injector D Such a system can take many forms. In FIG. 2 acamand-tappet pump A actuates a conventional metering valve B whichfeeds a charge of fuel through a smalldiameter conduit C to an ijector DFIG. 3 shows how an electromagentically actuated pump A can be used, andin FIG. 4 a rotary pump-valve A B is used. Systems are also known inwhich, for instance, a small electromagnetically actuated self-primingpump is mounted directly on the injector, so that elements correspondingto B and C are omitted.

FIG. 5 shows the circuit of an apparatus whose four networks A B C and Dcorrespond to the abovedescribed elements. The network A corresponds tothe pump or fluid-pulse generator and consists of a generaor G of pulsesof trapezoidal shape in series with which is connected an impedance Zreproducing the inherent lag or backflow resistance. Since a fluid pulseis a surge of fluid of a given volume, pressure and duration, therepresented parameter may be either the pressure or volume. The network3,, corresponding to the metering valve comprises a diode dshunted by aseries tuned circuit 1 c and by a load resistor r The pressure line issimulated by a conventional electronic delay circuit C Finally theinjector equivalent network D is formed of a series tuned circuit 1 cdamped by a resistor r;., with a series diode d and a resistor r actingas load.

The circuit of FIG. 6 represents an operational model of the presentinvention having four networks A -D corresponding to the similarlyidentified elements described above. Network A comprises an adjustablepulse generator 1 which forms trapezoidal pulses with parallel flanks,an impedance 2 (e.g. a potentiometer) whose value depends on signallevel and which is controlled by a reactive element 3 (e.g. a servomotorsee pp. 47 ff. Servomechanism Practice, McGraw-I-Iill Book Co., N.Y.,1960), and a variable capacitor C whose value determines theaccumulating volume of the pump. All of the characteristics of theabovedescribed pumps can be simulated with this network. Thus the heightof the pulse (amplitude) will represent pressure and the charge on thecapacitor will represent volume as a function oftime. The network Bincludes an inductance L connected in series with a capacitor C to forma tuned circuit shunted by an adjustable resistor Rpi, leveldiscriminators 4 and 5 which pass a signal when the amplitude thereofexceeds a predetermined level as with the threshold detector of U.S.Pat. No. 3,529,144) an operational amplifier 6 with adjustable feedbackresistor, and an adder 7. The network C comprises a conventionalchoke-capacitor type of delay line (see U.S. Pat. No. 2,830,179) typecells. Finally the fourth network D comprises an impedance whose valuedepends on the pulse level as controlled by a reactive element 9, aseries tuned circuit L C level discriminators 10, 11 (which pass asignal when the level thereof exceeds a predetermined value as with thethreshold detector of U.S. Pat. No. 3,529,144), and operationalamplifiers 12, 13 with nonlinear feedback. Coefficient potentiometersare shown at N. The devices 5 and 11 have additional inputs for thereference signal.

In operation the device functions as follows:

A parallel-flank trapezoidal impulse is delivered and as it appears atthe outut terminals (represented by arrowheads) of the pulse generator 1the impedance of element 15 (e.g. as described for impedance 2,) becomesinfinite to simulate the throttling effect of the pump inlet. Part ofthe originally formed pulse is drained to ground through the impedance 2controlled by the feedback elements 3 (responding to the potentialcapacitor) and C which are set according to the ac,- cumulating volumeof the pump simulated. In the simulation of injection systems as shownin FIGS. 2 and 3 with metering valves the switches K K and K are movedinto the left-hand, a position.

Since the pressure valve does not form a direct andimmediatecommunication link in the fuel-injection system the pulse then travelsthrough the passive elements L,, C,, and Rp, (delay network), thenthrough the discriminator 4, and the adder 7. One input to the latter(derived from amplifier 6) represents the component of direct build upin pressure of the fuel at the inlet to the transmission line while theother input (from discriminator 4) represents the lag produced at thevalve, the summer 7 forming a composite signal representing the slug offuel entering the transmission tube. Thence the signal (from summer 7)is fed through the delay circuit C whose delaying properties are tunedto simulate those of the pressure line, depending on this elementslength and cross-sectional area. To simulate systems with closedinjectors the switches K and K, are thrown into their left-hand, apositions. Initially the injector is not open so that the delay lineeffectively terminates at the impedance 8 whose value is great becausethe signal is small to start with. The impulse is reflected to the otherend since the line there has also a large impedance, and this reflectingback and forth oscillation conoutput-impedance adder 7, and thencethrough the delay line C which is ineffective until a condition cor.responding to valve opening comes into being.

The rise of the injectors needle: is simulated by passage of the pulsethrough the discriminator and L and C to ground and through thediscriminator 11, and operational amplifiers 12 and 13 whose feedbackscan be adjusted to simulate flow resistance in the valve orifice. In theinjection system being simulated the needle would now reach the limit ofits passage, a condition simulated by the tuned circuit L C whose timeconstant is adjusted to correspond to the rise time of such an injectorneedle. The discriminator 10 blocks this tuned circuit off so that thepulse only goes through discriminator 11 and amplifiers 12 and 13.

On completion of the pulse at the generator 1, the pulse length being ofcourse adjusted to correspond to that of the pump being simulated, theimpedance of element 15 drops to zero to discharge the condenser C andthe element 14 is triggered by the trailing pulse flank to couple thetuned circuit 1. C,, and Rp, with the delay line for precisedetermination of the extent of discharge of this element, whichcorresponds to the pressure remaining in the pressure pipe after firingof the injector. An impulse is obtained at the output terminal ofamplifier 13 whose waveform corresponds to that of the fuel-injectionthe cicuit was programmed to simulate, regardless of scale.

In the case of systems with an open injector the switches K and K areplaced in the right-hand, b positions in which case the pulse is feddirectly from the delay line C to the,input of amplifier 13.

For systems in which the pressure valve is part of the pump or notpresent at all the switches K, are switched into the right-hand, bposition and the net work B is replaced with a simple nonlinear element16 which shapes the pulse according to the size of the communicationorifice between pressure pipe and pump.

Finally in circuits without a pressure pipe the switch K is switchedfrom the left-hand, a positon to the righthand, b position to short outthe delay line C and allow for direct and immediate communicationbetween networks B and D 1 t Such an arrangement can be embodied as aconventional oscilloscope-type of equipment having a multiplicity ofadjustments for all of the parameters of a fuelinjection system. Say,for instance, that a given pump, metering valve, and injector are to beused. With the apparatus according to the present invention theadjustments of the delay line can be changed until the optimum output isachieved, then the readings noted and a pressure pipe of thosecharacteristics used. Furthermore the elements which wear and theparameters which change with time or varying temperature conditions areknown and can be tested on such a device before even building afuel-injection system in order to best gauge tolerances.

The system described above has numerous advantages which will be readilyapparent. Firstly, it insures the rapid and precise determination ofgeometric dimensions of the elements of the injection system to bedesigned, and which will then perform the given function. Secondly it isno longer necessary to produce a enegine and thus provides an optimumutilization of the latter, especially when it is operated by electronicfuel injection. Fourthly, thesystem allows calculation and visualizationof the influence of practically every element on the shape of the fuelpulse injected into the engine. Finally, it enables the influence ofwear of the elements upon the injection and of the determination ofcritical wear in a convenient and economical manner.

I claim:

1. A method of simulating the operating characteris- 10 tics of afuel-injection system in which a slug of fuel is produced and suppliedto a fuel injector, said method comprising the steps of:

generating an electrical pulse having a waveform analogous to the buildup of the fuel slug with time;

electronically shaping said electrical pulse by passing same through anonlinear network to represent the change in character of said fuel slugas the latter is fed to said fuel injector;

electronically delaying the shaped electrical pulse in accordance withfluid-transmission characteristics between the production of said fuelslug and the delivery thereof to said fuel injector;

reshaping the delayed electrical pulse in accordance with the operatingcharacteristics of said injector;

displaying the reshaped electrical pulse as a function of time; and

varying at least one parameter of said generated electrical pulse, theshaping of said electrical pulse, the delay of said electrical pulse andthe reshaping of 30 said electrical pulse to obtain an optimum waveformthereof afer reshaping.

2. An apparatus for simulating the operating characteristics of afuel-injection system in which a fuel slug is fed to a fuel injector,said apparatus comprising:

means for generating an electrical pulse havng a waveform analogous tothe build up of said fuel with time;

first elecronic means including a nonlinear network connected to thegenerating means for shaping said electrical pulse for simulating thetemporary blockage of flow of said fuel slug by a valve of thefuelinjection system; second electronic means including a delay lineconnected to the first electronic means for delaying the shapedelecrical pulse in accordance with transmission characteristics for saidslug of a pressure line between said valve and said fuel injector; and

third electronic means connected to said delay line for reshaping thedelayed electrical pulse in accordance with the operatingcharacteristics of said injector upon said fuel slug.

3. The apparatus defined in claim 2 wherein said generating meansincludes a variable-level square-pulse generator and a reactiveimpedance connected in series therewith and connected to said nonlinearnetwork.

4. The apparatus defined in claim 3 wherein said first elecronic meansincludes a variable circuit including an inductor in series with acapacitor to form a tuned network, a resistor ridged across said networkin parallel to the series-connected inductor and capacitor, and a diodeconductive in the direction of said delay line bridged across saidnetwork in parallel to the seriesconnectd inductor and capacitor.

5. The apparatus defined in claim 4 wherein the third electronic meansincludes a variable circuit including an inductor connected in serieswith a capacitor, a diode connected in series with a further resistorand connected to the series-connected inductor and capacitor of thethird electronic means and conductive away therefrom, and yet anotherresistor in parallel with the series-connected inductor and capacitor ofsaid third electronic means.

6. The apparatus defined in claim 2, further comprising switch meansconnectable across said first electronic means for connecting saidgenerating means directly to said delay line for simulating afuel-injection system without a valve.

1. A method of simulating the operating characteristics of afuel-injection system in which a slug of fuel is produced and suppliedto a fuel injector, said method comprising the steps of: generating anelectrical pulse having a waveform analogous to the build up of the fuelslug with time; electronically shaping said electrical pulse by passingsame through a nonlinear network to represent the change in character ofsaid fuel slug as the latter is fed to said fuel injector;electronically delaying the shaped electrical pulse in accordance withfluid-transmission characteristics between the production of said fuelslug and the delivery thereof to said fuel injector; reshaping thedelayed electrical pulse in accordance with the operatingcharacteristics of said injector; displaying the reshaped electricalpulse as a function of time; and varying at least one parameter of saidgenerated electrical pulse, the shaping of said electrical pulse, thedelay of said electrical pulSe and the reshaping of said electricalpulse to obtain an optimum waveform thereof afer reshaping.
 2. Anapparatus for simulating the operating characteristics of afuel-injection system in which a fuel slug is fed to a fuel injector,said apparatus comprising: means for generating an electrical pulsehavng a waveform analogous to the build up of said fuel with time; firstelecronic means including a nonlinear network connected to thegenerating means for shaping said electrical pulse for simulating thetemporary blockage of flow of said fuel slug by a valve of thefuel-injection system; second electronic means including a delay lineconnected to the first electronic means for delaying the shapedelecrical pulse in accordance with transmission characteristics for saidslug of a pressure line between said valve and said fuel injector; andthird electronic means connected to said delay line for reshaping thedelayed electrical pulse in accordance with the operatingcharacteristics of said injector upon said fuel slug.
 3. The apparatusdefined in claim 2 wherein said generating means includes avariable-level square-pulse generator and a reactive impedance connectedin series therewith and connected to said nonlinear network.
 4. Theapparatus defined in claim 3 wherein said first elecronic means includesa variable circuit including an inductor in series with a capacitor toform a tuned network, a resistor ridged across said network in parallelto the series-connected inductor and capacitor, and a diode conductivein the direction of said delay line bridged across said network inparallel to the series-connectd inductor and capacitor.
 5. The apparatusdefined in claim 4 wherein the third electronic means includes avariable circuit including an inductor connected in series with acapacitor, a diode connected in series with a further resistor andconnected to the series-connected inductor and capacitor of the thirdelectronic means and conductive away therefrom, and yet another resistorin parallel with the series-connected inductor and capacitor of saidthird electronic means.
 6. The apparatus defined in claim 2, furthercomprising switch means connectable across said first electronic meansfor connecting said generating means directly to said delay line forsimulating a fuel-injection system without a valve.